The thermoelectric material is a solid material which can convert thermal energy into electrical energy or use electrical energy to move heat. In 1821, Thomas Johann Seebeck found that a circuit made from two dissimilar metals (Cu and Bi), with junctions at different temperatures (ΔT) would generate an electric potential (ΔV), which is defined as Seebeck coefficient (S=ΔV/ΔT), and used as a principle for the thermoelectric generator and thermocouple. In 1835, Jean Charles Athanase Peltier found that an electrical current would produce heating or cooling at the junction of two dissimilar metals, and this principle was used for thermoelectric cooler. Twenty years later, William Thomson established the base of thermoelectric theory and predicted a third thermoelectric effect, now known as the Thomson effect. In the Thomson effect, heat is absorbed or produced when current flows in a material with a temperature gradient. The heat is proportional to both the electric current and the temperature gradient.
The thermoelectric material has been developed more than one hundred years so far. How to obtain better thermoelectric conversion efficiency was the most important goal for its applicability. Until 1954, Goldsmid and Douglas etc. applied semiconductor materials to thermoelectric coolers and successfully lowered down cooling temperature to 0° C., this huge progress induced a studying heat in 1960. However, for the past 30 years, this field has fallen in a difficult position. Until 1990, various novel materials have been developed so as to inspire studies in this field. Thermoelectric materials often involve the multi-component system, and complex composition and synthesis condition limit its utility. At present, it is a major object to develop novel thermoelectric materials and thermoelectric components.
In thermoelectric material developments, thermoelectric figure of merit (z=S2/κρ; S: Seebeck coefficient; κ=thermal conductivity, ρ=electrical resistivity) is an important indicator for developments. Nowadays the most popular commercial thermoelectric material is p-type semiconductor Bi2Te3, whose thermoelectric figure of merit is 1. Hsu etc. (Science, Vol. 303, pp. 818-821, 2004) has published a paper about high-performance thermoelectric material AgPbmSbTe2+m, which indicated that nano structure could help its thermoelectric conversion efficiency and its thermoelectric figure of merit reached 2.2 at 800K. Therefore, how to obtain better thermoelectric conversion efficiency has become a crucial object.